Patients with type 2 diabetes mellitus (T2-DM) have higher prevalence of no-reflow phenomenon - a poorly understood and unpredictable complication of percutaneous coronary intervention (PCI) in which diminished blood flow to distal microvascular beds persists despite the successful treatment of the occlusive lesion of the epicardial coronary artery. Current therapeutic interventions to prevent no reflow are ineffective. Preliminary observations related to this application led to my main hypothesis that small coronary arteries of diabetic patients exhibit a paradoxical constriction to sudden increases in flow, an alteration, which contributes to no reflow. I propose that RhoA-dependent co-localization of arginase I and eNOS leads to reduced NO synthesis and diminished NO-mediated dilatation in response to flow in T2-DM. I also hypothesize that stimulation of platelet endothelium cell adhesion molecule -1 (Pecam-1, known as primary flow sensor in endothelium) with increases in intraluminal flow elevates endothelial [Ca2+]i, which via inducing phospholipase A2 and arachidonic acid release leads to enhanced production of thromboxane A2 in coronary vessels of T2-DM patients. To test these hypotheses, I aim to isolate small coronary vessels from the (discarded) atrial appendages of patients with T2-DM undergoing cardiac surgery. Using small vessel pressure myography and videomicroscopy, diameter changes of the isolated, coronary arteriole (< 100 5m) exposed to sudden increase in intraluminal flow will be measured in the presence of inhibitors of specific signaling pathways. To investigate (co)localization of eNOS and arginase I as well as to detect spatial distribution and interaction of Pecam-1 laser scanning confocal microscopy and fluorescence resonance energy transfer approaches will be used in isolated, pressurized coronary arteries and coronary endothelial cells in culture. Moreover, flow-induced changes in endothelial [Ca2+]i will be measured with Fura-2 fluorescence in intact, pressurized coronary arterioles to reveal spatial differences of [Ca2+]i elevations at subcellular level. Should the results obtained in the course of the project support my hypothesis this will be the first description of Pecam-1-coupled constrictor prostanoid production in human coronary arteries. Results will also provide a novel mechanism by which spatial distribution of Pecam-1 determines the nature of vasoactive mediators released to increase in flow in T2-DM. Data obtained in this project will also help to develop novel avenues for effective therapeutic strategies, such as the use of prostanoid inhibitors at the time of PCI, to prevent no reflow in patients with T2-DM.